In January 2007, Insight Magazine, a right-wing publication, reported that Clinton's team had questions about Obama's Muslim background. It said that researchers connected to Clinton were spreading the allegation that he spent four years in a madrassa. The Clinton campaign said this was not true.

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And back on March 19, 2007, then-Clinton adviser Mark Penn wrote a strategy memo to Clinton about Obama. It did not raise the issue of Obama's citizenship. But it did identify Obama's "lack of American roots" as something that "could hold him back."

Reggie Love, the longtime traveling aide to Obama, wrote in his book that Clinton and Obama had a heated conversation about the notion that Clinton supporters were sending emails saying that he was a Muslim.

In a March 2008 interview with "60 Minutes," Clinton said she took then-Sen. Obama's word that he was not a Muslim, but when pressed if she believed he was, she replied, "No. No, there is nothing to base that on -- as far as I know."

What we see in 2008 from Clinton is a subtle stoking of questions about Obama's identity, but she never went as far as Donald Trump did in 2011 in an interview with Fox News.

"He doesn't have a birth certificate. He may have one, but there's something on that, maybe religion, maybe it says he is a Muslim. I don't know. Maybe he doesn't want that," said Trump in the 2011 interview.